The competing renewal application is for the SWEDEN Clinical Center of The Environmental Determinants of Diabetes in the Young (TEDDY) study. The primary objective of this multi-center, multi-national, epidemiological study is the identification of infectious agents, dietary factors, or other environmental exposures that are associated with increased risk of islet autoimmunity and type 1 diabetes mellitus (T1D). TEDDY is an observational cohort study in which newborns who are less than 4.5 months of age and have high risk HLA genotypes in the general population or are first-degree relatives of patients affected with T1D will be enrolled. The specific aims of this SWEDEN Clinical Center renewal application are to: 1) Complete this Center's contribution to the HLA-DR.DQ screening of 361,000 newborns and enrollment of 7,800 high- risk infants into intensive prospective follow-up to achieve the overall TEDDY goals. 2) Refine strategies to retain subjects enrolled in the follow-up and collect all planned biological specimens and epidemiological data according to the standard protocol including close monitoring of performance and sample/data quality. 3) Ascertain prospectively development of islet autoantibodies and clinical T1D in the study subjects. 4) Perform planned laboratory tests at appropriate times using a nested case-control study design to answer specific scientific questions and hypotheses pertinent to the TEDDY study goals. 5) Analyze and publish laboratory and epidemiological data in collaboration with the TEDDY Data Coordinating Center (funded by a separate contract). 6) Guide the ongoing TEDDY project by participation of the Clinical Center investigators and staff in work of the study Steering Committee and sub-committees. Recruitment stared in September 2004 and will continue until December 31, 2009. Eligible children are followed four times per year until 4 years of age and twice a year thereafter until 15 years of age. The frequency of eligible newborns in Sweden is as high as 7.9% and the rate of enrollment is 70% in both the general population and among first degree relatives. The SWEDEN Clinical Center is contributing 37% of the 3500 children enrolled in the study so far. Three children have developed T1 D. Participants will be followed to age 15 years. Identification of environmental factors will lead to a better understanding of disease pathogenesis and result in new strategies to prevent, delay or reverse T1 D.